JPH0578918A - Production of ultra-thin tape-like carbon fiber - Google Patents

Abstract

PURPOSE:To obtain the subject carbon fiber having a thickness thinner than a specific level and excellent compressive strength, tensile properties and productivity by polymerizing a condensed polycyclic hydrocarbon, etc., in the presence of hydrogen fluoride, etc., melt-spinning the obtained optically anisotropic pitch and infusibilizing and carbonizing the spun fiber. CONSTITUTION:A condensed polycyclic hydrocarbon or a material containing the hydrocarbon is polymerized at 200-400 deg.C in the presence of hydrogen fluoride and boron trifluoride catalyst to obtain an optically anisotropic pitch having an optical anisotropy ratio of >=90%, a softening point of 200-280 deg.C and a spinning viscosity of 400-500 poise. The pitch is melt-spun through a slit nozzle and the obtained pitch fiber is infusibilized under a tension of 0.005-0.05g/d and carbonized to obtain the objective carbon fiber having a thickness of <=3mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a tape-shaped ultra-thin carbon fiber which is extremely thin and has physical properties such as low electric resistance and high compressive strength.

[0002]

2. Description of the Related Art Carbon fibers were originally made of rayon as a raw material, but at present, due to their characteristics and economical efficiency, polyacrylonitrile (PAN) fibers are used as raw materials for PAN-based carbon fibers and coal or It is replaced by pitch-based carbon fiber made from petroleum-based pitches. Of these, pitch-based carbon fibers have been attracting attention because they are economically superior, and in particular, pitch-based carbon fibers made of optically anisotropic pitch as a raw material have excellent properties such as high strength and high elastic modulus. At the same time, it is known that physical properties such as volume resistivity are superior to PAN-based carbon fibers.

It has also been found that higher physical properties are exhibited by controlling the internal structure of pitch-based carbon fibers (Japanese Patent Laid-Open No. 59-53717). That is, the sectional structure of the pitch-based carbon fiber is radial,
There are random, onion structures, etc., for example,
The radial structure is not preferable because cracks easily occur and the physical properties deteriorate due to macro defects. The factors that influence the cross-sectional structure include the nozzle structure, the spinning temperature,
There is viscosity during spinning. However, for example, in the case of carbon fibers obtained by spinning with a specific slit nozzle and having an elliptical cross section, the tensile properties are improved (JP-A-61-1).
No. 08725), no improvement effect can be seen in physical properties such as volume resistivity.

It has also been found that reducing the fiber diameter changes the cross-sectional structure and reduces the probability of microdefects, thereby improving the physical properties of carbon fibers.

However, when the fiber diameter is reduced or the nozzle shape is changed from a perfect circle to a special irregular shape, the spinnability is extremely deteriorated and it is often difficult to form a fiber. .. Therefore, it is substantially difficult to make the fiber diameter of conventional coal and petroleum pitch-based carbon fibers smaller than the fiber diameter of PAN-based carbon fibers.

[0006]

Means for Solving the Problems The inventors of the present invention have made diligent studies to solve the above problems, and as a result, 1) As a pitch for melt spinning, JP-A-1-139621
Based on the method described in Japanese Patent Publication No. JP-A No. 2004-187, an optically anisotropic substance is obtained by polymerizing a condensed polycyclic carbon hydrogen or a substance containing the same in the presence of hydrogen fluoride and a boron trifluoride catalyst at 200 to 400 ° C. The content of the natural phase is 90% or more and the softening point is 200 ° C to 280 ° C (preferably 220 ° C to 26 ° C).
0 ° C) pitch is produced, and 2) spinning is performed using a slit nozzle at a low spinning temperature such that a high viscosity of 400 to 5000 poise (preferably 800 to 2000 poise) is obtained during spinning of melt pitch, Further, the pitch fiber is rapidly cooled with a cooling gas such as N ₂ immediately below the nozzle, and 3) at the time of infusibilization, the fiber is 0.005 to 0.05.
It has been found that when a tension of g / denier is applied, followed by carbonization and graphitization, ultrathin carbon fibers with a thickness of 3 μm (preferably 2 μm) or less can be obtained.

That is, the present invention provides the following method for producing a tape-shaped ultra-thin carbon fiber: Condensed polycyclic hydrocarbon or a substance containing the same is used in the presence of hydrogen fluoride and a boron trifluoride catalyst.
After polymerization at ℃, the obtained optically anisotropic pitch is melt-spun from a slit nozzle to infusibilize and carbonize the obtained pitch fiber. Carbon fiber manufacturing method.

2. Item 2. The method for producing a tape-shaped ultra-thin carbon fiber according to Item 1, wherein the optically anisotropic amount of the optically anisotropic pitch is 90% or more and the softening point is 200 ° C to 280 ° C.

3. Upon melt spinning, the spinning viscosity is 400-
5. The method for producing a tape-shaped ultrathin carbon fiber according to the above item 1, wherein the poise is 5000 poise.

4. When infusibilized, the pitch fiber is 0.00
The method for producing a tape-shaped ultrathin carbon fiber according to the above item 1, wherein a tension of 5 to 0.05 g / denier is applied.

The ultrathin carbon fiber of the present invention has a uniform thickness of 3 μm or less over the entire width direction and can be said to be a tape-shaped fiber. As a result of measuring the physical properties of such an ultra-thin fiber, it was unexpectedly found that the volume resistivity was considerably lower than that of pitch-based carbon fiber which is generally commercially available. At the same time, it was found that the compressive strength and the tensile properties were remarkably improved. Furthermore, since the thickness is as thin as 3 μm or less, the infusibilization rate during production is considerably higher than that of the conventional pitch fiber.

The pitch used as a raw material in the present invention has an optical anisotropy amount of 90% or more and a softening point of 200 to 200 produced by the method described in JP-A-1-139621.
If the pitch is 280 ° C., the softening point is 220 to 26.
The thing of 0 degreeC is more preferable. Also, the pitch is 50% by weight
It is also possible to use a blend pitch in which the above and the rest are other resins.

The spinning nozzle has a slit shape,
Nozzle width (L) and nozzle height (H) are not particularly limited, but normally L is around 0.4 to 1.6 mm, H
Is sufficient if it is 0.06 to 0.14 mm. By reducing H, the thickness of the fiber that can be formed also decreases, but if H is less than 0.06 mm, the spinnability is extremely reduced, which is not preferable.

Conventionally, the spinning is usually 50 to 3 because the pitch exhibits an appropriate spinning viscosity and the spinnability is good.
It was performed with a low viscosity of about 100 poise. However, when spinning is performed at such a viscosity, the pitch fiber cross section becomes elliptical or circular due to the low viscosity, whichever slit nozzle is used. When the temperature is lowered and the high-viscosity spinning is carried out in order to obtain a thin tape-shaped fiber corresponding to the nozzle shape, the spinnability is deteriorated and the fiber is not formed.

On the other hand, in the present invention, when a specific pitch is spun by a specific spinning method, a tape-shaped fiber having a uniform thickness of 3 μm or less can be spun. That is, in order to obtain a uniform thickness using the pitch specified above, it is preferable to perform spinning with a viscosity as high as possible, and the viscosity is preferably 400 to 5000 poise. In particular, in order to obtain a uniform thickness and not impair the spinnability, 800 to 20
More preferably, it is 00 poise.

[0016] Further, 0 to 5 pitch fibers are provided under the nozzle.
It is desirable to quench with a gas such as N ₂ cooled to about 0 ° C. However, since the spinnability of the fiber is not hindered by gas, it is necessary to set the gas amount to an appropriate amount that does not cause yarn breakage.

The spinning method is not particularly limited, and conventionally-used melt spinning, air sucker method, vortex method and the like can be adopted.

At the time of infusibilization, 0.005 to
By applying a tension of 0.05 g / denier, the thickness can be made more uniform and thin. However, when a tension of 0.1 g / denier or more is applied,
The fiber may be broken, which is not preferable.

Further, in the infusibilizing step, since the fibers are thin, the infusibilization is completed more quickly than in the case of the fibers having the same area in cross section, that is, circular or elliptical. That is, since the penetration distance of oxygen from the fiber surface to the central portion at the time of infusibilization is short, the infusibilization time can be shortened by about 60 to 80% as compared with the case of perfect circular and elliptical fibers. The degree of shortening becomes more remarkable as the fiber thickness becomes smaller. Such shortening of the infusibilization time significantly reduces the cost, and thus has a great effect.

The infusibilization method is not particularly limited, and commonly used infusibilization in air or infusibilization using an oxidizing agent such as nitric acid or nitrogen dioxide can be employed.

Finally, after the above-mentioned treatment, carbonization and graphitization are carried out in an inert gas atmosphere while applying a tension to the infusible fiber so as not to break the yarn.
A tape-shaped ultra-thin carbon fiber having a uniform thickness can be manufactured. The temperature conditions at the time of carbonization and graphitization are not particularly limited, about 1000 to 2000 ° C. at the time of carbonization, and 2000 to 30 at the graphitization.
The temperature may be about 00 ° C. Even in the carbonization and graphitization steps at 1000 ° C. or higher, if the pitch specified in the present invention is used, the fiber further shrinks. That is, in the thickness direction between carbonization and graphitization, the pitch fiber finally shrinks by about 20 to 60% and becomes thin. This shrinkage rate is large compared to the case where the conventional raw material pitch is used.

[0022]

The tape-shaped ultra-thin carbon fiber obtained by the present invention is a fiber whose cross section has a uniform thickness of 3 μm or less, and is characterized by particularly low electric resistance as well as improvement in compressive strength and tensile properties. There is. Moreover, at the time of production, good spinnability is maintained even with a high viscosity, and since the shrinkage rate is high in infusibilization, carbonization and graphitization, it is possible to stably obtain an ultrathin fiber. Further, since the fibers are thin, the infusibilization time can be shortened, and the productivity is dramatically improved.

[0023]

EXAMPLES Examples and comparative examples will be shown below to further clarify the features of the present invention.

The properties of the product were measured by the following methods.

1. Softening point Measured using a softening point measuring device manufactured by Swiss Metra.

2. Optical anisotropy amount The area ratio of the anisotropic structure was calculated from the polarization micrograph.

3. Tensile test and volume resistivity According to JIS R-7601 "Carbon fiber test method", measurement with a strand was performed.

4. Cross-sectional shape of fiber The fiber diameter was measured by scanning electron micrograph, n = 2
The average value of the width and thickness of the 0 cross section was calculated.

5. Compressive strength It carried out according to JIS K-7076 "compression test method of carbon fiber reinforced plastic".

[0030]

Example 1 Based on the method described in JP-A-1-139621, 1 mol of naphthalene, 0.5 mol of HF and 0.5 mol of BF ₃ were charged into a 500 ml acid-resistant autoclave at a reaction pressure of 25 kg / While keeping it at cm ² G,
The temperature was raised to 260 ° C. and the reaction was carried out at 260 ° C. for 2 hours. Then, HF and BF ₃ were recovered in a gaseous state, and then nitrogen was blown to remove low boiling point components to obtain pitch. The yield of the obtained pitch was 76% by weight. The softening point of this pitch was 251.5 ° C., and it was confirmed by a polarization microscope that the pitch was 100% anisotropic.

This pitch is L = 1.0 mm, H = 0.1 mm
273 when spun using the slit nozzle of
It could be spun at a winding speed of 450 m / min for 10 minutes without breakage. The spinning viscosity at that time was about 1200 poise. Further, nitrogen was blown at a position of 2.5 mm below the nozzle at a rate of 2 l / min to quench the pitch fiber.

Next, the pitch fiber was heated to 270 ° C. at a rate of 8 ° C./min while a tension of 0.01 g / denier was applied,
It was made infusible by holding it for 10 minutes.

The infusibilized fiber was heated in an inert gas at 15 ° C.
1400 ° C., 2000 ° C. and 26 at a heating rate of 1 / min
The temperature was raised to 00 ° C., and carbonization and graphitization were performed while applying a tension not to break the fibers. The physical properties are shown in Table 1.
Shown in.

[0034]

[Comparative Example 1] Spinning was performed under the same conditions as in Example 1 except that a perfect circular nozzle (diameter 0.2 mm) was used,
The infusibilization was (a) fibers carried out under the same conditions as in Example 1 or (b) the temperature was raised to 270 ° C. at 8 ° C./min, and the temperature was raised to 25
The fibers held for minutes were fired at 2000 ° C. Table 1 shows the physical properties at that time.

[0035]

[Table 1]

As is clear from the results shown in Table 1, according to the method of the present invention, the effect of shortening the infusibilizing time of the ultrathin fibers and the improvement in volume resistivity, compressive strength and tensile properties are remarkably observed.

[0037]

Example 2 Using the same pitch as in Example 1, L = 1.3
After winding at a winding speed of 620 m / min using a slit nozzle of 5 mm and H = 0.06 mm, 8 ° C / up to 260 ° C.
The temperature was raised in minutes, and the temperature was maintained for 5 minutes for infusibilization. After that, baking was performed at 2000 ° C. in an inert gas. The cross-sectional shape of the obtained carbon fiber has a thickness = 0.95 μm and a width = 17.2.
was μm. Table 2 shows the physical properties of the obtained ultra-thin carbon fiber.

Table 2 Volume resistivity 1.62 × 10 ⁻⁴ Ω · cm Tensile strength 501 kg / mm ² Elastic modulus 46 ton / mm ²

[0039]

[Third Embodiment] L = 0.9 mm, H with the same pitch as in the first embodiment.
= 0.20 mm slit nozzle was used and spinning was performed while changing the winding speed. That is, spinning was performed at a winding speed of 300, 600 and 900 m / min, but spinning was not possible at 600 and 900 mm / min. The fiber spun at 300 m / min was made infusible under the same conditions as in Example 1 and fired at 2000 ° C. The results are shown in Table 3. The cross-sectional thickness of this fiber is 3.9.
The physical properties were low, with a width of 5 μm and a width of 12.3 μm. It can be seen that the features of the present invention are lost when the sectional thickness is 3 μm or more.

Table 3 Volume resistivity 15.0 × 10 ⁻⁴ Ω · cm Tensile strength 330 kg / mm ² Elastic modulus 38 ton / mm ²

Claims (4)

[Claims] 1. A condensed polycyclic hydrocarbon or a substance containing the condensed polycyclic hydrocarbon in the presence of hydrogen fluoride and a boron trifluoride catalyst.
After polymerization at ˜400 ° C., the obtained optically anisotropic pitch is melt-spun from a slit nozzle, and the obtained Bitch fiber is infusibilized and carbonized.
A method for producing a tape-shaped ultra-thin carbon fiber having a size of m or less. 2. The optical anisotropy amount of the optically anisotropic pitch is 9
The method for producing a tape-shaped ultra-thin carbon fiber according to claim 1, wherein the softening point is 0% or more and the softening point is 200 ° C to 280 ° C. 3. The melt spinning has a spinning viscosity of 400 to 50.
The method for producing the tape-shaped ultra-thin carbon fiber according to claim 1, wherein the poise is 00 poise. 4. The pitch fiber is 0.005 to 5% when infusibilized.
The method for producing a tape-shaped ultra-thin carbon fiber according to claim 1, wherein a tension of 0.05 g / denier is applied.